1. Field of the Invention
This invention relates to mechanical pipe connectors, and more particularly to connectors for interconnecting sections of large tubular piling
2. Description of the Prior Art
The production of oil and gas from offshore wells has grown into a major endeavor of the petroleum industry, and this growth has led to the development of means for drilling and completing wells, and for recovering petroleum products therefrom, in offshore locations where it is desirable to locate drilling and production platforms or wharfs. These platforms may be anchored to the sea floor by mechanical tubular piles driven into the sea floor and connected to the platform. Each of the piles may be from a few feet to over a thousand feet in length, depending upon the depth of the water at the offshore location. The handling of the large tubular piling is made considerably easier by building up the piles from several 100-150 foot long sections joined together in an end-to-end manner. A connector which adjoins two adjacent sections must be rugged, reliable, and easy to assemble and disassemble.
Prior art connectors most commonly used for this purpose include the interrupted screw thread variety. The interrupted screw thread connector has several limitations: (1) it is expensive to machine; (2) it requires great care in handling to prevent damaging the threads; (3) precision alignment is required during connection and disconnection; and (4) the pipe must be rotated to complete the assembly which requires that a large amount of torque be applied. The fact that the pipe must be rotated to complete the assembly is by far the greatest shortcoming of this prior art connector, and huge mechanical contrivances weighing many tons have been designed and built just to accomplish this rotation in an offshore environment. As the pile diameters approach 60 or more inches this rotation becomes almost impossible to accomplish because of the high torque required to rotate one section of pile while connecting or disconnecting it to an adjacent section.
Another type of prior art pile connector which has been tested for offshore use employs a snap-type locking ring for securing the two portions of the connector together. This connector has experienced failures because improper loading of the locking ring results in a high stress concentration in the machined receptacles into which the ring is positioned. The locking ring also has a tendency to vibrate into an unlocked position caused by vibrations as the pile sections are driven into the seafloor
Other prior art drivable pile connectors use radially engageable dogs to secure one section of piling to the next section. The engageable dog type connector preloads the connection to secure the piling sections together; however, the vibrations which develop during offshore driving of piles may cause the connector to vibrate loose thereby relieving its preload. This vibration can cause radially movable threaded screws which are used in these connectors to seize and gall, thereby preventing the screws from being rotated after the driving operation. Also, the dogs tend to become brittle and are subject to bending or breaking because of small imperfections machined in the connectors used with the dogs. Because such dogs must be moved in a radial direction to disengage one section of piling from another, an excessive amount of space must be provided in the connectors for them.
During the stabbing operation of the connector halves it is undesirable that the halves fit tightly together during early portion of the stabbing stroke. Close engagement should be limited to the final few inches of travel as the halves are engaged.
In order to function satisfactorily, a pile connector must have sufficient strength to withstand the repetitive high tension and compressive stresses experienced under actual driving conditions. However, it has been shown that small amounts of "slack" in the pile connector do not contribute adversely to a loss of pile strength or to the loss of driving energy, and in some cases this slack contributes to the reduction of tension loads on the connector that are due to the reflection of the compression wave from the pile tips, and thus a rigid pile connector is not necessarily required for piling.